The present invention relates to wireless communications, and more particularly to a DC compensation system for a wireless communication device configured in a zero intermediate frequency (ZIF) architecture that utilizes a DC control loop to enable direct conversion of radio frequency signals to baseband frequency.
Network communication is a growing area of technology both for business and home applications. A network system enhances communication and provides a suitable environment for enhanced productivity and capabilities both at home and in the workplace. The Internet for example, is a global, mostly wired, communication network that couples devices together on a world-wide basis that enables world-wide communication between any devices coupled to the Internet. The Internet enables access to a plurality of services, such as file sharing, faxing, chat, email and information access via websites to files, libraries, databases, computer programs, etc.
Many businesses and commercial entities include a relatively established and sophisticated network environment for enhanced productivity and communication. For example, Extranets or Intranets provide enhanced yet protected or secure communication to a selected group of people on the Internet. Many small businesses and homes are coupled to the Internet via some variation of local area network (LAN) or the like. It is becoming more advantageous and common for small businesses and home environments to include LAN capabilities to connect to the Internet or to access other services, such as file sharing, printing, faxing, etc. and to further enable communication such as via chat and email services, and the like and to provide access to common databases and libraries, etc. Many such small networks are connected through a set of wires. For example, a network may be established in a small office or home through standard phone wires. Phone wires are already available in each office of a business and in several rooms of a typical home. Technology also exists to establish network communications via power lines which are typically available in every room of a house. Many small offices and homes may alternatively be wired with network wires, such as a twisted-pair telephone wires with corresponding RJ-45 connectors utilized by various Ethernet embodiments.
Wired networks provide a certain level of convenience but have many limitations. Each device coupled to the network must be attached to a corresponding wire through which the network is established. The location of each device, therefore, is limited to enable access to the network wires. Cable management is also a significant issue, since devices must be placed to enable proper routing of wires. It is desired that the wires be conveniently placed and for aesthetic reasons, out of sight. Wires should be located in such a manner as to reduce or eliminate any chance of accidental interference or disconnect or hazards such as tripping. Once wired devices are properly placed, movement of the devices is very limited or otherwise not practical without substantial re-configuration or re-routing of the wires. Maintenance of wired network devices can be inconvenient and often requires that the wires be removed during service and then reconnected properly.
Certain wireless technologies are known, such as infrared technology. Infrared technology works well for certain applications, such as remote control systems or the like. For network applications, infrared technology is a relatively inexpensive option but has certain limitations, including limited bandwidth, range limitations, and line-of-sight issues. Infrared technology has been utilized in certain applications, such as access points (APs) and point to point relay nodes to extend a network down hallways and the like. For example, infrared devices are known for use in hospitals, hotels and other relatively large structures. The APs or nodes, however, are usually fixed and located in such a manner, such as on the ceiling, to avoid potential interference with physical objects. Due to line of sight issues, infrared technology is not particularly convenient for network communications at the end points of the network where human interaction is necessary.
Radio frequency (RF) technology appears to be the technology of choice for establishing a viable wireless local area network (WLAN). RF technology for LAN systems, however, is not particularly optimized for small office or home use. Wireless technology is established for industrial and commercial uses and applications such as courier services, vehicle rentals, warehouse operations and inventories, etc. The wireless embodiments for commercial and industrial applications are too expensive or otherwise specialized and thus are not suited for direct use in the small office or home environment.
The Bluetooth technology is being developed for application in the home or office. Bluetooth technology offers relatively limited bandwidth at very low cost to enable connectivity and network communications between certain communication devices, such as cellular phones, computer systems including notebook, laptop and desktop computers and further including other hand-held devices such as personal digital assistants (PDAs) or the like. The Bluetooth technology, however, has limited bandwidth and therefore relatively low data throughput capability. The consumer market demands higher data throughput and reliability such as is necessary for DVD and other multimedia applications.
The typical environment for a WLAN is very noisy and not optimal for wireless communications. For example, most homes include many electronic devices resulting in an electronically noisy environment that may interfere with WLAN communications, such as microwave ovens, garage door openers, radios, television sets, computer systems, etc. Further, the communication medium between wireless devices constantly changes. For example, most environments or rooms include multiple reflective surfaces creating multipath noise in the wireless environment. Furthermore, movement of items or devices or the like such as hands, bodies, jewelry, mouse pointers, etc. or activation of electronic devices, such as cooling fans or the like, affects the overall wireless communication path and potentially degrades wireless communication performance.
Low cost and low power wireless communication devices for enabling a WLAN system or the like for use at home or in the small business is desirable. It is further desired to provide low cost and low power wireless communication devices for any type of wireless system for any type of application. The system must be relatively robust with significant performance and be capable of significant data throughput.
The present invention combines a DC offset correction signal with an input modulated signal to form a properly DC adjusted input modulated signal. A DC compensation system for a wireless communication device configured in a zero intermediate frequency (ZIF) architecture according to the present invention includes a combiner that combines a DC offset signal from an input signal and that provides an adjusted input signal. The wireless communication device includes DC control logic that generates the DC offset signal, gain control logic that attempts to keep the input signal power at a target level, and a gain interface that converts gain levels between the gain control logic and the DC control logic.
In a primary signal path of the wireless device, a gain amplifier receives the adjusted input signal and provides an amplified input signal based on a gain adjust signal. The gain control logic includes a gain feedback circuit that receives the amplified input signal, that estimates input signal power and that provides the gain adjust signal in an attempt to maintain the input signal power at the target power level. The DC control logic includes a DC estimator that estimates a DC level in the amplified input signal and that provides a DC estimate signal. The DC control logic also includes a DC amplifier that receives the DC estimate signal and that provides the DC offset signal based on a gain conversion signal. It is noted that the gain of the DC amplifier may be less than one (e.g. 1/G) and may operate as an attenuator. It is understood that xe2x80x9camplificationxe2x80x9d includes the operation of attenuation. The gain interface includes a gain converter that receives the gain adjust signal and that provides the gain conversion signal to the DC amplifier.
The gain interface may perform one or more functions. In one embodiment, the gain converter converts between gain ranges of the gain amplifier and the DC amplifier. Alternatively, or in addition, the gain converter converts between logarithmic and linear gain scales when the gain amplifier has a logarithmic gain scale and the DC amplifier has a linear gain scale.
In a more specific embodiment, the wireless communication device includes a radio frequency (RF) circuit, a ZIF transceiver and a baseband processor. The RF circuit receives and provides an RF signal, and may include one or more antennas, switches, filters and matching networks to receive and deliver the RF signal to the transceiver. The ZIF transceiver includes an RF mixer circuit that converts the RF signal to a baseband input signal, a combiner that combines a DC offset from the baseband input signal to provide an adjusted baseband input signal, and a baseband amplifier that receives the adjusted baseband input signal and that asserts an amplified input signal based on a gain adjust signal. The baseband processor includes gain control logic, DC control logic and a gain interface. The gain control logic receives the amplified input signal, estimates input signal power and asserts the gain adjust signal in an attempt to keep the input signal power at a target power level. The DC control logic estimates an amount of DC in the amplified input signal and provides the DC offset in an attempt to reduce DC in the amplified input signal. The gain interface converts gain levels between the gain control logic and the DC control logic. The DC control logic operates to remove or otherwise eliminate DC from the received signal that is provided to conversion and decode logic in the baseband processor. `The RF circuit and the ZIF transceiver generally operate with analog signals while the baseband processor primarily uses digital logic. Appropriate conversion devices are included to establish interfacing, such as analog to digital converters (ADC) and digital to analog converters (DAC). The RF signal may include in-phase (I) and quadrature (Q) portions, where the RF mixer circuit splits I and Q baseband input signals from the RF signal. Operation is substantially identical for both I and Q channels. Two separate summing junctions are provided, one each for the I and Q channels. The baseband amplifier includes separate I and Q channel baseband amplifiers, which are both controlled by the same gain adjust signal from the gain control logic to ensure proper I and Q channel tracking. Separate DC control logic and gain interfaces are provided for the I and Q channels, where operation is substantially the same. The DC control logic operates to remove or otherwise eliminate DC from the received signal that is provided to a spreading decoder and a packet decoder in the baseband processor.
A method of reducing DC in a wireless ZIF device includes converting a received radio frequency (RF) signal to a baseband signal, subtracting a DC offset from the baseband signal to achieve an adjusted baseband signal, amplifying the adjusted baseband signal based on a gain signal to achieve an amplified input signal, estimating a power level of an input baseband signal from the amplified input signal, adjusting the gain signal to achieve a target power level of the input baseband signal, measuring a DC level of the amplified input signal to obtain a DC estimate, amplifying the DC estimate based on a gain conversion signal to provide the DC offset, and generating the gain conversion signal based on the gain signal.
The method may further comprise converting between gain ranges and/or converting between different gain scales, such as between logarithmic and linear gain scales. The method may further include subtracting the DC offset from the baseband signal. The amplifying the DC estimate may comprise attenuating the DC estimate. The attenuating may further include inverting the DC estimate to provide the DC offset, where the DC offset is then added to the baseband signal.
It is appreciated that removal of the IF portion of a high performance wireless transceiver, with proper DC compensation, results in a relatively high performance, low cost wireless ZIF transceiver with reduced power requirements. The use of a DC compensation loop interfaced to the gain loop according to embodiments of the present invention achieves these goals. Such capability enables a WLAN system to be designed for use at home or in the small business that is relatively robust and that has significant performance with relatively high data throughput operation.